A stable adaptive flux observer for a very low speed-sensorless induction motor drives insensitive to stator resistance variations

In recent years, numerous attempts have been made to improve the performance of sensorless induction motor drives. However, parameter variations, low-speed and zero-speed operations are the most critical aspects affecting the accuracy and stability of sensorless drives. This paper presents a stable adaptive flux observer (AFO) for sensorless induction motor drives insensitive to stator resistance variations. Design of the observer feedback gain of AFO is proposed to guarantee the stability, especially at low speeds. The adaptive law parameters are designed to give quick transient response and good tracking performance. The sensitivity of AFO to stator resistance mismatch is studied. A stator resistance adaptation scheme for accurate speed estimation at low speeds is derived. The relation between the identification error of rotor speed and adaptive gains is clarified based on Lyapunov theory. Experimental setup using DSP-DS1102 control board is implemented. Simulation and experimental results confirm the efficacy of the proposed approach.